Water swellable coatings and method of making same

ABSTRACT

A method for forming a water swellable coating and a water swellable coating for forming a coated substrate are provided. The water swellable coatings are semi-gel dispersions of particulate superabsorbent polymer in a polyvinyl chloride plastisol. A dispersion is formed from the polymer and plastisol, then contacted with a substrate and heat cured to a semi-gel state. The coatings are capable of swelling in the presence of water to protect the substrates from water penetration, block water from penetrating the coatings to reach other substrates or to retain water to prevent leakage.

FIELD OF THE INVENTION

The present invention relates to the field of water swellable coatings,more particularly to semi-gelled water swellable coatings formed from adispersion of superabsorbent particulate polymer in a liquid polyvinylchloride plastisol.

BACKGROUND OF THE INVENTION

Super absorbent polymers (SAP) are compounds capable of swelling to manytimes their original weight by absorbing water. SAPs are used, amongother things, as an absorbing compound for baby diapers, in protectingpower and communication cables, in agriculture for use in increasing thecapability of soil to retain moisture and nutrients, and in the hygienicpackaging of food products with absorbent pads. SAPs swell upon exposureto water, and in many instances, are capable of absorbing up to 500times their weight in water. The SAPs are typically used in powder formor in a composite form in which SAP particles are blended with finefibers and then entrapped within a fibrous mat.

In the past, attempts have been made to use the SAPs to form coatings onsynthetic fiber used in the manufacturing of cable, such as fiber opticcable. The coated synthetic fiber was used in place of preexistingsynthetic fiber components for cable. The intention was that the coatingwould swell upon exposure to water and fill gaps in the cable renderingthe cable watertight to protect the fiber optic component. The presentinventors attempted to provide SAPs to the cable in the form of a fullyfused solid dispersion of SAP in a polyvinyl chloride (PVC) plastisolcoated fiber. The PVC plastisol included PVC resin in suspension in aplasticizer. However, the fully fused dispersion in fiber optic cablesdid not perform satisfactorily, because the SAPs do not swell at asufficient rate when subjected to pressurized water. The fused, solidPVC plastisol matrix functions to restrain the ability of the SAP toswell.

To form these dispersions, SAP powder was blended with liquid PVCplastisol formulation. The plastisol formulation was converted from itsliquid state to a homogeneous solid plastisol through fusion of theplasticizer and PVC at elevated fusion temperatures of about 121° toabout 170° C. or more to fully cure the dispersion. Synthetic fiberswere coated with the fused dispersion and then used in the manufactureof fiber optic cable as a filler, binder, strength member and similaruses.

A further application of SAP in a coating formulation includes anemulsion of SAP in an oil-in-water emulsion as described in U.S. Pat.No. 5,342,686. This coating formulation may be used for light coatingson KEVLAR substrates, but is not suitable for heavier SAP coatings, suchas those required to block penetration of water into coaxial cable.Further, the emulsion uses solvents which may be detrimental in manycoating applications and/or harmful to the enviroment.

While the SAP/PVC dispersions for use as swellable coatings wereessentially comparable with other prior art fillers, a need in the artremains for an improved SAP coating composition which is capable ofusing more of the swelling capabilities of the SAPs and expanding thepotential uses for SAP coatings. There is also a need in the art for amethod of forming an SAP coating composition which provides maximumwater absorption properties. In addition, it would be desirable toachieve a coating composition useful on synthetic fibers, syntheticwoven and unwoven fabrics and other substrates which swell at a ratesufficient to protect the substrate from penetration of water.

SUMMARY OF THE INVENTION

The invention includes a water swellable coating, and a coated or atleast partially impregnated substrate which includes a water swellablecoating on a surface, or within voids, of the substrate. The coatingcomprises a semi-gel dispersion of a particulate SAP in a PVC plastisol,and substantially blocks the penetration of water through the coatingand/or retains water. The present invention also includes a method formaking a coated substrate.

The method includes preparing a dispersion including a particulate SAPand a liquid plastisol which includes a PVC resin and a plasticizer. Thesubstrate is contacted with the dispersion to form a coating layer onthe substrate, or to at least partially impregnate the substrate. Thecoating layer is heat cured for a period of time sufficient to form awater swellable, semi-gel coating layer on the substrate. The coatinglayer may at least partially impregnate the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of the preferred embodiments of the invention,will be better understood when read in conjunction with the appendeddrawings. For the purpose of illustrating the invention, there are shownin the drawings embodiments which are presently preferred. It should beunderstood, however, that the invention is not limited to the precisearrangements and instrumentalities shown. In the drawings, like numeralsare used to indicate like elements throughout. In the drawings:

FIG. 1 is a partially broken away perspective view of a synthetic fibercoated in accordance with the present invention;

FIG. 2 is a cross-sectional view of a synthetic fabric coated inaccordance with the present invention;

FIG. 2a is a partially broken away greatly enlarged sectional view of aportion of the sythetic fabric of FIG. 2;

FIG. 3 is a schematic representation of a method for making a coatedfiber in accordance with the present invention;

FIG. 4 is a schematic representation of a method for making a coatedfabric in accordance with the present invention;

FIG. 5 is a plot of absorption capacity of water swellable coatedpolyester yarn in distilled water against time for both a prior artfully fused coating --▪-- and a semi-gel coating --▴-- according to theinvention; and

FIG. 6 is a plot of absorption capacity of water swellable coatedpolyester yarn in tap water against time for both a prior art fullyfused coating --▪-- and a semi-gel coating --▴-- according to theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Certain terminology is used in the following description for convenienceonly and is not limiting. The words "right," "left," "lower" and"upper," designate directions in the drawings to which reference ismade. The terminology includes the words above specifically mentioned,derivatives thereof, and words of similar import.

The coatings of the present invention may be used on a wide variety ofsubstrates, including, for example, synthetic fiber materials, such aspolyamide, polyaramid, polyester, fiberglass, carbon, polyolefin,polyacrylic and rayon; natural fibers such as cotton, metallic fiberssuch as carbon and steel fibers, synthetic woven and nonwoven fabricsformed of materials such as those mentioned with respect syntheticfibers which may be used for making filters, awnings, carpets andtextiles; synthetic films, polymeric components, metals, metal alloys,wood, concrete, composites, paper and the like. The coatings may be usedon any substrate to which the coatings will sufficiently adhere suchthat they do not easily peel off. Further, such coatings are useful in awide variety of applications in which it is important to prevent wateror other liquids from passing through or reaching a substrate.

Such applications include the coating of coaxial cable to render thecable watertight, the coating of fiber fillers for use inside cable toprevent water from damaging fiber optics, or the coating of fabrics orfilms to prevent water from passing through a laminate structure. Due tothe wide variety of uses for the present coatings, for the purpose ofdescribing the preferred embodiments of practicing the present inventionand the best mode, the detailed description is directed to the preferredembodiments of using the coating of the present invention on syntheticfiber material and a synthetic fabric substrates. However, it will beunderstood from this disclosure that the present invention is notlimited to use on these particular substrates.

While the water swellable coatings are described herein as capable offorming a coating layer on a substrate, it will be understood from thisdisclosure that, in many coating applications, the coating will at leastpartially impregnate a substrate, such as a fiber material, to form awater swellable impregnate within at least an outer portion of thesubstrate. As such, use of the terminology "coating" should beinterpreted to include within its meaning surface coating and/or atleast partially impregnating a substrate with the semi-gel dispersion asdescribed below.

Referring now to the drawings in detail, there is shown in FIG. 1 acoated substrate, generally designated as 10, including a fibersubstrate 12 and a water swellable coating 14 in accordance with thepresent invention. In FIG. 2, a water swellable coating 14 is providedto one exterior surface 16 of a synthetic fabric substrate 18 to form acoated substrate 10' in accordance with the present invention. It willbe understood by those of ordinary skill in the art, from thisdisclosure, that both surfaces 16, 20 of the fabric 18 may be coatedwith a water swellable coating according to the present invention. Asshown in FIG. 2a, the fabric 18 may contain voids 21 which can bepenetrated, or impregnated, by the coating 14. The water swellablecoating 14 substantially blocks the penetration of water through thecoating to protect the substrate. As shown in FIGS. 1 and 2, the coating14 includes a semi-gel dispersion of a particulate SAP 22 in a PVCplastisol 24. The particulate polymer 22 is shown greatly enlarged fordescriptive purposes.

The coating may partially impregnate the substrate, as shown in FIG. 2a,or it may impregnate a fiber bundle in voids between fibers. The coatingfurther may function to protect the substrate which it coats, or toprotect another substrate, for example, the coating may be used on afibrous filler substrate which is used to protect a further substratesuch as a fiber optic core. The coatings on the small filler fibersswell upon exposure to water and expand to block water penetrable gapsbetween the coated filler fibers. The coatings retain water which hasalready filled the gaps between the filler fibers and retains that waterwhile preventing further water penetration. It is in applications suchas this that the absorption rate of the coating is important. If thecoating does not absorb water fast enough, it will penetrate the gapsbetween the coating harming the fiber optic core before the coatingswells to its full potential.

A further function of such a coating is to act as a water retainingcoating. An example of such a water retaining application includescoating a fiber which may be used in the manufacture of diapers. Thefiber would swell to retain water and also function to block water frompassing out of the diaper.

The coating includes a semi-gel dispersion of a particulate SAP in a PVCplastisol. The SAP may be any of various superabsorbent polymers havingan average particle size of about 500 microns, where average particlesize is measured in the largest dimension of the particle. The particlesize may be smaller or larger depending upon the particular applicationfor the coating. Preferably, the average particle size is from about 1to about 500 microns. and the polymer is in a powder form. In addition,the polymers are preferably at least partially cross-linked. Suitablepreferred SAPs include salts of polyacrylate-based polymers. The saltswhich may be used in forming the SAPs include sodium, potassium andammonium. The preferred SAPs for use in the present invention includehomopolymers and copolymers of sodium and potassium polyacrylates. Otheruseful polymers include starch grafted sodium polyacrylate and partialsodium salt of polypropenoic acid.

When coating a substrate such as a synthetic fiber, cord, strand, rope,braid or any other synthetic fiber material or a fine synthetic fabricwhich will be exposed to water or other liquid environments, preferablythe SAP is a sodium polyacrylate homopolymer with an average particlesize of no greater than about 100 microns. Such polymers can be foundcommercially as CABLOC 80HS available from Stockhausen Inc., Greensboro,N.C.; AQUA KEEP J-550-SF available from Sumitomo Seika Chemical Company,Ltd., Japan; and SANWET IM1000F available from Hoechst Celanese.

When coating a heavier substrate, for example a heavier syntheticfabric, or for coating substrates such as synthetic fiber materials orfine synthetic fabrics which will be exposed to a higher electrolyticconcentration in the surrounding liquid to be absorbed, for example saltwater or waste water with a significant ion content, the SAP preferablyhas a larger average particle size of from about 100 to about 300microns. Suitable SAPs useful in such applications include potassiumcopolymers of polyacrylate and polyacrylamide in which the copolymer iscrosslinked. Suitable commercial SAPs for such use include CABLOC 100Favailable from Stockhausen, Inc., Greensboro, N.C.

The SAPs according to the present invention are hydrophilic polymerscapable of absorbing and retaining a comparatively large quantity ofwater. The polymers include water binding groups, for example carboxylicacid groups. The salt ions of the acrylate-based polymers, as used inthe present invention, are located at the carboxylic acid groups pendantfrom the polymer carbon backbone. The carboxylic acid groups aresolvated when contacted with water, or other aqueous liquids, formingmany charged ionic groups which repel each other. The polymer chain, inthe presence of water, or other liquid, expands and unfolds such that itcan absorb more liquid. While such a polymer may otherwise dissolve, aslight crosslinking present in the SAP chains used in the presentinvention prevents them from completely dissolving. When used in powderform, the SAPs exposed to water contain the water and form a gel.

In the coating according to the present invention, the SAP is dispersedin a liquid polyvinyl plastisol. The liquid plastisol includes a PVCresin and a plasticizer. The liquid plastisol may be purchasedcommercially as a plastisol formulation or independently synthesized.Preferably, for most fiber coating applications, the plastisol used, iffully fused to a solid, would have a Shore hardness of from about 10Shore A to about 90 Shore A hardness, preferably about 50 Shore A. It isalso preferred that the liquid plastisol used have a relatively lowviscosity as the dispersion of the particulate superabsorbent polymer inthe plastisol will significantly increase viscosity. As such, the liquidplastisol preferably has the consistency of a pourable liquid and aviscosity of from about 500 to about 40,000 cp, preferably about 1,000to 4,000 cp.

While an organosol may be used, or the viscosity of the plastisoladjusted with an organic solvent which is later volatilized, it is notpreferred to use solvent based materials in the present invention due toconsiderations of toxicity, volatility and environmental impact ofsolvent-containing compounds.

The resin within the liquid plastisol may be any PVC dispersion resin ora blend of PVC dispersion and blending resins as long as the viscositycriteria of the plastisol are satisfied.

The plasticizer may also be any suitable plasticizer useful in PVCplastisols, however, the plasticizer must be selected to meet theviscosity criteria for the plastisol. Suitable plasticizers for theliquid plastisol to be used in the present invention includedi-2-ethylhexyl phthalate (DOP), dihexyl phthalates, dibutyl phthalates,alcohol phthalates, dioctyl adipate (DOA), phosphate esters such astricresyl phosphate, octyldiphenyl phosphate and trioctyl phosphate,dioctyl adipate, dioctyl sebacate, trioctyl trimellitate, andtriisooctyl trimellitate, as well as blends or mixtures of these andother similar plasticizers. Preferably, the plasticizer used is DOP orDOA.

The plasticizer and PVC resin are preferably present in the liquidplastisol in a range of weight percentage ratios of resin to plasticizerof from about 0.25:1 to about 3:1, more preferably about 1:1. It will beunderstood from this disclosure that more or less resin or plasticizercan be provided for variations in the resulting properties of thepresent SAP dispersion as long as the resulting coating can be providedin a semi-gel form.

The plastisol may optionally include additives such as secondaryplasticizers, flame retardants, stabilizers, fillers, colorants,viscosity modifiers, foaming agents and combinations of these additives.

Suitable secondary plasticizers may include, for example, those listedabove, aliphatic hydrocarbons, epoxidized soya, oils and/or other knownplasticizers.

Stabilizers are preferably capable of neutralizing hydrogen chloride, adecomposition product of PVC. Suitable stabilizers include, for example,mixed metal salts, such as barium-cadmium-zinc-based,barium-cadmium-based and cadmium-zinc-based stabilizers and organic tinstabilizers. Preferably, the mixed metal salt stabilizers are used.Light and UV stabilizers, such as 2-hydrobenzophenones, aryl-substitutedacrylates and p-aminobenzoates can also be provided.

Other suitable additives include antimony derivative flame retardants,colorants such as pigments, titanium dioxide, zinc oxide and carbonblack, and fillers such as calcium carbonate, asbestos, clay, talc,silica and the like. Viscosity modifying additives may also be providedas long as the resulting plastisol has a viscosity suitable for formingthe dispersion in accordance with the present invention.

If the dispersion is to be foamed for other water swellableapplications, foaming agents can be added and the dispersion foamed by asuitable foaming method.

The additives should be provided to the plastisol in amounts of fromabout 0.1 to about 10 parts by weight per hundred parts by weight ofplastisol.

The dispersion of SAP in the liquid plastisol should include from about10 weight percent to about 50 weight percent of particulate SAP. If morethan about 50 weight percent SAP is provided to the dispersion, thedispersion consistency is too dry or paste-like, and less than 10 weightpercent is not sufficient SAP to effectively swell. More preferably, thedispersion includes about 30 weight percent SAP.

The coating of the present invention is a semi-gel dispersion. Once theparticulate SAP is dispersed in the liquid plastisol, the dispersionbecomes a semi-gel by heat curing for a period of time sufficient topartially gel the plasticizer and the PVC resin.

PVC resin plastisols generally fuse at temperatures between 121°-177° C.when a homogeneous "hot melt" stage is achieved. To form a solidplastisol, the hot melt phase is cooled to below a temperature of about50°-60° C. Such a plastisol is fully cured after fusion. As temperatureincreases, PVC plastisol liquid goes through gelation and then fusion bypassing through a series of polymer stages, including wetting of thesuspended polymer particles in the plastisol liquid by the plasticizer,diffusion of the plasticizer into the particles, disappearance ofboundaries between the particles, flowing together of the PVC polymerand melting of the crystallite structure with molecular flow achieved.

In the SAP dispersion of the present invention, as temperatureincreases, the plastisol begins to undergo the stages described above inthe following approximate increments: (A) at temperatures up to about35° C., the plasticizer wets the PVC particles; (B) at temperaturesbetween about 35° C. and 50° C., the plasticizer diffuses into the resinparticles; (C) at temperatures between about 50° C. and 90° C., theparticle boundaries begin to disappear and the PVC flows together; and(D) at temperatures between about 90° C. and 170° C., the crystallitesof PVC polymer fuse together.

The level of gellation is controlled in forming the present waterswellable coatings to between stages (B) and (D) above. Between thesephases, the coating partially undergoes gellation and has not yet fusedsuch that a "semi-gel" phase of the dispersion is achieved. If theprocess were continued to full fusion and the resin cured in the mannerof forming PVC plastisols generally, and in the manner of prior artattempts to form water swellable coatings, the water swellableproperties would be detrimentally affected. The resulting coatedsubstrates had a slow rate of absorption and low absorption capacity.Coated fibers exhibited high yarn stiffness and reduced yarn breakstrength.

In the present invention, by forming a semi-gel dispersion, the waterswellable coatings achieve faster rates of absorption, and higherabsorption capacities in comparison with prior art fully fused coatings.Further, water swellable yarns formed with the present coatings haveincreased flexibility and higher breaking strength in comparison withprior art coatings.

The water absorption capacity of the coatings are measured by submerginga layer of coating in distilled water and determining the weight ofwater absorbed after the elapse of a specific period of time. The weightof water is divided by the weight of the coating to provide theabsorption capacity for that time period. The absorption rate isdetermined as the absorption capacity divided by the length of time ofexposure. For a 0.011 inch thick planar layer of coating, the thicknessbeing measured in a direction perpendicular to the plane of the layer,the absorption capacity is preferably at least about 34 g water/gcoating in distilled water after a 5 minute period. More preferably, thecoatings achieve an absorption capacity of at least about 40 g water/gcoating for a 5 minute period of exposure of a 0.011 inch thick sample.

On coated substrates, the absorption capacity is measured in terms ofthe weight of water absorbed in grams divided by the weight of thecoated substrate after the elapse of a specific period of time. Theabsorption rate is then determined by dividing the absorption capacityby the time of exposure.

The semi-gel coating when applied to substrates such as fiber, yarn,braid and the like as described above, provides a softer, more flexiblecoating than a fully fused coating. The semi-gel coated yarn exhibits arelatively flat cross-section in comparison with a fully-fused coatedyarn which exhibits a harder, stiffer coating having a rounder or ovalcross-section. The flat yarn cross-section is beneficial in applicationssuch as a binder yarn for fiber optic cables as the flat profilegenerally does not interfere with the uniformity of the cable diameter.The lower stiffness of the semi-gel coating also helps to minimize therisk of line breakage in the cable as it does not tend to spring fromthe line in the manner of prior art coated fillers.

The reduced break strength of yarn coated by the present invention ismost likely the result of the stiffer coating. In addition, due to thelower % elongation, and lower stiffness, the present invention providesmore material for the same cost by having a higher yield as measured inlength of yarn/unit weight.

When the plastisol is taken to the semi-gel state, upon heat curing, theplastisol does not age harden such that it remains in the same semi-gelstate as processed. The semi-gel matrix enables the SAP to expand toachieve high levels of swelling in the presence of water or otheraqueous liquids. The SAP can then perform its function of hydrogenbonding with the water or other liquid to retain the water andsubstantially block further penetration through the coating to thesubstrate or through voids between coated substrates which surround awater-sensitive material, such as the fiber optic cable filler describedabove. The SAP can also function merely to retain water in an absorbencyapplication as in baby diapers.

The method of forming a coated substrate in accordance with the presentinvention will now be described with respect to the coating of asynthetic fiber material and a fabric referring to FIGS. 3 and 4. Withreference to FIG. 3, one or more windings 24 of a synthetic fibermaterial 26 are drawn, under tension, by any suitable method, over astationary bar 27 through a bath 28 of a dispersion 30 of particulateSAP in a liquid PVC plastisol. Additional stationary bars may beprovided, or the stationary bar 27 may be replaced by one or morerollers. However, a stationary bar 27 is preferred to rollers tominimize fiber breakage. Preferably the dispersion bath 28 iscontinuously agitated to provide uniform dispersion to the fiber 26.

The dispersion 30 continuously overflows the bath 28 into a holding tank32 and is continuously supplied to the bath 28 by gravity feed throughline 33 from feed tank 34. The dispersion is pumped by a pump 36 throughline 38 to the feed tank 34 and recirculated to the bath 28. In thecoating of fiber materials, the plastisol in the bath 28 tends to bedepleted. The rate of depletion of the plastisol in the bath ismonitored by evaluating the absorption capacity of the material in theholding tank 32. The plastisol in the dispersion to be recirculated fromthe holding tank is replenished by providing an amount of plastisol tothe feed tank 34 through line 40 based on the absorption capacity of thedispersion in the holding tank 32. The absorption capacity increases asthe viscosity increases. Viscosity increases as the concentration ofplastisol decreases in the dispersion in comparison to the concentrationof SAP. As such, the absorption capacity is a preferred criteria forevaluating the rate of plastisol depletion. Viscosity may be directlymonitored, but is generally not as accurate in determining theappropriate rate of plastisol depletion. By adding the plastisol to thefeed tank 34 at a rate proportional to the rate of depletion, asubstantially constant concentration of resin is maintained in the feeddispersion.

When beginning the method, the dispersion is formed in the feed tank byproviding the particulate SAP 42 gradually to the liquid PVC plastisol44, while providing continuous agitation to the plastisol dispersion inthe feed tank 34. The SAP is preferably added at an average rate ofabout 20 to about 25 lb particulate polymer, preferably in the form of apowder, per minute. The rate of addition may vary in accordance with thesize of the feed tank 34 and amounts of components used. The dispersionis preferably mixed by a heavy duty high torque mixer at a low speed ofabout 100 to about 1,500 rpm, preferably at a rate of about 750 rpm.

The fiber leaves the bath 28 with a coating and passes through an oven46. Excess plastisol is preferably wiped from the fiber by use of a die,pad, roll or other suitable means. The oven may be a convection,conduction or infrared oven, for example. Preferably, an infrared ovenis used having elements capable of temperatures of about 1,000° F. (538°C.). The oven chamber achieves an average ambient temperature betweenthe elements of from about 200° F. (93° C.) to about 450° F. (232° C.).The temperature of the oven and the residence time in the oven arecontrolled to maintain a coating temperature of between about 50° C. toabout 90° C., depending upon the PVC plastisol used, to achieve asemi-gel state for the PVC plastisol. Residence time in the oven iscontrolled by varying the speed of the fiber 26. Preferably, the fiberspeed is controlled to between 55 ft/min and 65 ft/min. The fiber leavesthe top of the oven after heat curing the coating to a semi-gel stateand is wound up as a coated substrate on take-up rolls 48. A pluralityof feed rolls 24 and take-up rolls 48 may be used in the present methodfor providing a water swellable coating. In addition, more than oneoven, bath, holding tank and feed tank may be provided. It will beunderstood by one of ordinary skill in the art that the fiber coatingprocess may be varied as long as viscosity, resin concentration, SAPconcentration, fiber speed and oven temperature are adequatelycontrolled to form a semi-gel coating on the fiber.

In FIG. 4, a roll 50 of synthetic fabric 52 is unwound, under tension,by any suitable method and drawn below a feed tank 54 to provide acontinuous flow of a dispersion of a particulate SAP in a liquidpolyvinyl resin dispersion as described above to the upper surface ofthe fabric 52. The feed tank 54 is subject to continuous agitation underlow shear conditions, and the dispersion is formed, as described abovewith respect to the method shown in FIG. 3 and the coatings of thepresent invention. The dispersion is smoothed by a doctor blade 56, orsimilar smoothing apparatus, to provide a smooth coating to the fabric52. The fabric is then drawn through an oven 58, such as that describedabove, wherein the temperature of the oven and the speed of the fabricare controlled to provide a semi-gel cure to the coating. The coatedfabric leaves the oven and is wound on take-up roll 60 as shown.

The method for forming a coated fabric may be varied, for example, toprovide coating to both sides of the fabric by pulling the fabricthrough a bath and smoothing the coating with opposing tension rolls,however, the coating parameters must be controlled to provide a semi-gelcoating to the fabric.

The invention will now be described in more detail with respect to thefollowing specific, non-limiting examples:

EXAMPLE I

Polyester yarn samples (Experimental Samples 1-6) coated with semi-gelcoatings of a dispersion including 30 weight percent CABLOC 80HS and 70weight percent Plastomeric DBX 3590N PVC were measured for absorptioncapacity in distilled water as measured in g distilled water/g coatedsubstrate. The yarn samples were cut into lengths of about 1 inch andweighed. About 2.00±0.01 g of the yarn are stirred with 100 ml ofdistilled water for 10 min. The mixture is filtered for 15 minutes andthe amount of water recovered is measured. The absorption capacity iscalculated by dividing the difference of the amount of water recoveredfrom 100 by the weight of the yarn. The same test was performed for thesame type of polyester yarn (Comparative Samples 1-6) coated with fullyfused coatings of the same dispersion, fused at a temperature of 170° C.for 5 min an air circulating oven. The absorption capacity was measuredfor the Comparative Samples in the same manner as for the ExperimentalSamples. The results of these tests showing the absorption capacity atvarious time intervals appears below in Table I. A comparison of theincrease in absorption rate of the Experimental Samples over theComparative Samples of a prior art fully fused coating is showngraphically in FIG. 5 where the triangular data points --▴-- present theExperimental Samples and the square data points --▪-- represent theComparative Samples.

                  TABLE I                                                         ______________________________________                                                       Absorption Capacity                                                                         Absorption Capacity                              Sample                                                                              Time     Experimental Samples                                                                        Comparative Samples                              No.   (sec)    (g water/g yarn)                                                                            (g water/g yarn)                                 ______________________________________                                        1      15      21.5          15.5                                             2      30      24.5          18.0                                             3      60      26.0          20.0                                             4      90      27.5          20.5                                             5     120      30.0          21.0                                             6     300      32.5          24.5                                             ______________________________________                                    

The results clearly show the significant increase in absorption rate andabsorption capacity of the water swellable yarn made in accordance withthe invention and the prior art water swellable yarn.

EXAMPLE II

150 lb of CABLOC 80HS were gradually added to a 55 gallon tank equippedwith a low shear Lightnin mixer, over a 15 minute period, to 350 gallonsof a dispersion of liquid PLASTOMERIC DBX 3590 N while continuouslymixing the dispersion. The weight percentage ratio of resin toplasticizer in the plastisol was approximately 1:1. The dispersion wascontinuously stirred at 750 rpm. 64 rolls of polyester were unwound andpulled at a rate of 60 ft/min through a bath of the dispersion. Theabsorption capacity was maintained at a minimum of 30 times fordistilled water. The rate of depletion of plastisol was determined to be20 lb/hr. A corresponding amount of plastisol was added to the tank toprovide a substantially constant concentration of plastisol in the tank.The bath was continuously agitated at a rate of 100 rpm. The coatedpolyester fiber was pulled through a Glenro RADPLANE infrared ovenhaving elements at 1000° F. (537° C.). The residence time in the ovenwas 5 seconds and the coating was cured to a semi-gel state. The coatedpolyester was wound on 64 take-up rolls. The coated polyester fiber hada minimum absorption capacity of 12 g distilled water/g coated fiberwhen submerged in distilled water for 5 min, a breaking strength of 35lb and a % elongation of 15%.

EXAMPLE III

A coaxial cable having a water swellable coating was formed by a dipcoating process using the dispersion of Example II and curing thecoaxial cable in the same oven as used in Example II at a temperature1100° F. (593° C.) by pulling the cable through the oven at a rate of 15ft/min. The coating on the coaxial cable exhibited an absorptioncapacity of 4.4 g distilled water/g coated coaxial cable when submergedin distilled water for 5 min.

EXAMPLE IV

A section of synthetic/cotton blend woven fabric 5 in wide×5 inlong×0.010 in thick was coated with the dispersion of Example II. Theexcess dispersion was scraped with a steel blade which also smoothed thecoating on one side of the fabric. The coated fabric was heated in anair circulating oven for 5 min at 140° C. to provide a coated fabrichaving a thickness of 0.012 in, corresponding to a coating thickness of0.002 in. The coated fabric sample was 67 percent by weight fabric and33 percent by weight coating. The absorption capacity of the coatedfabric after 10 minutes in distilled water was 22 g distilled water/gcoated fabric.

EXAMPLE V

Two bobbins of coated polyester fiber were made, an Experimental bobbinhaving the coating as described in the Experimental Samples of Example Iand a Comparative bobbin having the coating as described in theComparative Samples of Example I. Samples 7-11 were taken from eachbobbin and tested for break strength and elongation in accordance withASTM D2256. The results appear in Table II below and include the meanvalue and standard deviation (SD) for Experimental Samples 7-11 andComparative Samples 7-11.

                  TABLE II                                                        ______________________________________                                               Experimental Samples                                                                            Comparative Samples                                           Break               Break                                                     Strength Elongation Strength                                                                             Elongation                                Sample   (lb)     (%)        (lb)   (%)                                       ______________________________________                                         7       35.0      9.8       32.0   16.1                                       8       36.0     10.4       33.0   16.5                                       9       37.0     11.0       32.0   16.1                                      10       36.0     10.2       34.0   16.9                                      11       37.0     10.6       33.0   16.5                                      Mean     36.2     10.4       32.8   16.4                                      SD        0.84     0.45       0.84   0.33                                     ______________________________________                                    

The results show that the break strength of the Experimental Samples isabout 10% greater than the Comparative Samples made in accordance withprior art fully fused coatings. Further, the Experimental Samples show a36% lower elongation percent at break than the Comparative Samples.

EXAMPLE VI

Example I was repeated for Experimental Samples 12-17, with theexception that the absorption capacity was measured in tap water to showthe effect of electrolytes in tap water on absorption capacity andabsorption rate. The absorption capacity results appear in Table IIIbelow, and the increase in absorption rate achieved by the ExperimentalSamples are shown in FIG. 6, where the triangular data points --▴--represent the Experimental Samples and the square data --▪-- pointsrepresent the Comparative Samples.

                  TABLE III                                                       ______________________________________                                                       Absorption Capacity                                                                         Absorption Capacity                              Sample                                                                              Time     Experimental Samples                                                                        Comparative Samples                              No.   (sec)    (g water/g yarn)                                                                            (g water/g yarn)                                 ______________________________________                                        12     30      12.3           6.7                                             13     60      13.0          10.7                                             14     90      14.7          11.3                                             15    120      15.7          12.0                                             16    300      17.3          13.3                                             17    600      18.0          14.0                                             ______________________________________                                    

While the effect of the tap water electrolytes can be seen by comparingthe data of Table I and Table III, it is clear from the data in TableIII and FIG. 6, that the Experimental Samples 12-17 still show asignificant increase in absorption rate and capacity in comparison withprior art coatings of Comparative Samples 12-17. It took over 600 s forthe Comparative Samples to reach their maximum absorption capacity of14.0, whereas the Experimental Samples reached a 14.0 absorptioncapacity in only 80 s and continued on to a maximum of 18.0, i.e., 28.5%greater. In applications where the speed of absorption is critical, suchas for water-blocking of coaxial or fiber optic cable, this increase inabsorption rate is highly significant. Based on Table III, it can beseen that even in brackash waters where electrolytes play a role, asignificant increase in absorption capacity is achieved.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

We claim:
 1. A water swellable coating, comprising a semi-gel dispersionof a particulate superabsorbent polymer which is hydrophilic and capableof absorbing and retaining a large quantity of water in a polyvinylchloride plastisol.
 2. The water swellable coating according to claim 1,wherein the particulate superabsorbent polymer is selected from thegroup consisting of at least partially cross-linked homopolymers andcopolymers of sodium polyacrylate, and potassium polyacrylate.
 3. Thewater swellable coating according to claim 2, wherein the particulatesuperabsorbent polymer is sodium polyacrylate homopolymer having anaverage particle size of from about 1 to about 500 microns.
 4. The waterswellable coating according to claim 3, wherein the particulatesuperabsorbent polymer is sodium polyacrylate homopolymer having anaverage particle size of from about 1 to about 100 microns.
 5. The waterswellable coating according to claim 2, wherein the particulatesuperabsorbent polymer is a potassium copolymer of polyacrylate andpolyacrylamide having an average particle size of from about 1 to about500 microns.
 6. The water swellable coating according to claim 1,wherein the polyvinyl chloride plastisol comprises a polyvinyl chlorideresin and a plasticizer, the weight percentage ratio of the resin to theplasticizer being from about 0.25:1 to about 3:1.
 7. The water swellablecoating according to claim 6, wherein the weight percentage ratio of theresin to the plasticizer is about 1:1.
 8. The water swellable coatingaccording to claim 5, wherein the plastisol further comprises anadditive selected from the group consisting of secondary plasticizers,flame retardants, stabilizers, fillers, colorants, viscosity modifiers,foaming agents and combinations thereof.
 9. The water swellable coatingaccording to claim 1, wherein the coating comprises from about 10 weightpercent to about 50 weight percent superabsorbent polymer.
 10. The waterswellable coating according to claim 1, wherein the absorption capacityof the coating is at least about 34 g water/g coating after a 5 minuteexposure of a 0.011 inch thick layer of the coating to distilled water.11. The water swellable coating according to claim 10, wherein theabsorption capacity of the coating is at least about 40 g water/gcoating after a 5 minute exposure of a 0.011 inch thick layer of thecoating to distilled water.